The JSON serializer can deal with most .NET serializable object types, so it’s easy to pass back most custom objects as well as arrays and types of collections (inherited from IDictionary). Unfortunately though, Microsoft moved support for DataTable and DataSet to the Futures release so if you plan on using the 1.0 release only, you have to move any data into objects first or create your own jsonSerialization type converters.
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asp.net ajax 1.0不支持返回dataset和datatable